There are a variety of known robotic gripping devices in the prior art. These robotic gripping devices includes systems which may be pneumatically, hydraulically, or motor controlled. Typically, current robotic applications use a sensor mounted within the gripper assembly to detect part or work piece presence. That sensor or an additional sensor may be used to measure the grip pressure being exerted by the robotic gripper assembly. This is particularly true in applications where the robot gripper assembly is servo controlled. For example, U.S. Pat. No. 5,671,962 to Otsuka et al teaches a bi-finger robot gripping assembly wherein the robot controller receives a signal from a work detector attached to one of the fingers. The signal of the work detector indicates whether or not a work piece exists between the fingers. In operation, the controller calculates an output torque of the servomotor necessary for obtaining a computed optimum holding force on the basis of reference tables stored in memory and controls the servomotor accordingly.
U.S. Pat. No. 4,579,380 to Zaremsky et al teaches force servoing of an electric motor powered robot gripper. Force servoing is accomplished by providing a force transducer integral with one or more mounting blocks for monitoring the load exerted on one of the gripping fingers through a pivot and lever action of the mounting bracket positioned adjacent to the force transducer. An optical shaft encoder provides precise position information for position servoing tasks and a limit switch, located above one of the finger mounting blocks, is used to identify a known marker pulse on the encoder and serves to protect the device from damage which might occur from moving the blocks beyond the positions for which the device is designed.
U.S. Pat. No. 4,533,167 to Johnson teaches a robotics manipulator arrangement having a control system which allows the manipulator to be controlled with respect to the gripping force applied to an object. Johnson's arrangement utilizes a fluid pressure source such as a pneumatic source, a transducer responsive either to pressure or flow, and the variable fluid flow restriction means which is variable in response to the gripping force. The force is generated by the robotics manipulator gripping an object and varying the restriction means so that a changing fluid pressure can be sensed and used for control purposes.
The prior art fails to teach a robotic gripping system and method wherein work piece detection and gripper force can be determined without the addition of detectors/sensors, or the interface components required to interface such detectors/sensors with the robotic controller.